Method for separating and recovering 2,3,3,3-tetrafluoropropene and hydrofluoric acid

ABSTRACT

The present invention relates to a method for separating a composition containing 2,3,3,3-tetrafluoropropene and hydrofluoric acid, and for recovering the thus-separated 2,3,3,3-tetrafluoropropene and hydrofluoric acid. The invention also relates to a method for manufacturing and purifying 2,3,3,3-tetrafluoropropene using a hydrofluorination reaction of the saturated or unsaturated compound having three carbon atoms and including at least one chlorine atom in the presence of a fluorination catalyst.

This application is a Continuation of U.S. patent application Ser. No.14/131,036 filed Jun. 5, 2014, now allowed; which is a National Stageapplication of International Application No. PCT/FR2012/051327 filedJun. 14, 2012; which claims the benefit of French Application No.1156208, filed Jul. 8, 2011.

The present invention relates to a process for the separation of acomposition including 2,3,3,3-tetrafluoropropene and hydrofluoric acidand for the recovery of the 2,3,3,3-tetrafluoropropene and hydrofluoricacid thus separated.

The choice of a heat-transfer fluid is dictated, on the one hand, by thethermodynamic properties of the fluid and, on the other hand, byadditional constraints. Thus, a particularly important criterion is thatof the impact of the fluid under consideration on the environment.

The problems presented by substances which deplete the atmospheric ozonelayer were dealt with at Montreal, where the protocol was signalimposing a reduction in the production and use of chlorofluorocarbons(CFCs). This protocol has formed the subject of amendments which haverequired the abandoning of CFCs and have extended regulation to otherproducts, including hydrochlorofluorocarbons (HCFCs).

The refrigeration and air conditioning industries have invested a greatdetail in the replacement of these refrigerants and it is because ofthis that hydrofluorocarbons (HFCs) have been marketed.

In the motor vehicle industry, the air conditioning systems of thevehicles sold in many countries have moved from a refrigerant comprisingthe chlorofluorocarbon (CFC-12) to that of the hydrofluorocarbon(1,1,1,2-tetrafluoroethane: HFC-134a), which is less harmful to theozone layer. However, from the viewpoint of the objective set by theKyoto protocol, HFC-134a (GWP=1430) is regarded as having a high heatingpower. The contribution to the greenhouse effect of a refrigerant isquantified by a criterion, the GWP (Global Warming Potential), whichsummarizes the heating power by taking a reference value of 1 for carbondioxide.

2,3,3,3-Tetrafluoropropene (HFO-1234yf), as a result of its low GWP, isconsidered a potential candidate for the replacement of HFC-134 in motorvehicle air conditioning.

2,3,3,3-Tetrafluoropropene is generally prepared by reacting achlorinated or fluorinated/chlorinated hydrocarbon compound in thepresence of a greater than stoichiometric amount of hydrofluoric acid(WO 2008/054781; WO 2008/040969). Thus, the stream of conclusion in thisreaction comprises not only HFO-1234yf but also a not insignificantamount of HF.

The document WO 2011/059078 provides for the recovery of the HFO-1234yffrom the mixture at the outlet of the hydrofluorination reaction bycooling said mixture in order to obtain an upper phase concentrated inHF and a lower phase concentrated in HFO-1234yf, followed by azeotropicdistillation of the lower phase.

This document is concerned only with the purification of HFO-1234yf. Inpoint of fact, it is found that the upper part concentrated in HFcomprises a large amount of HFO-1234yf. Consequently, this upper partshould also be subjected to a treatment if it is desired to recover HFin order to be reused in the hydrofluorination reaction withoutneedlessly recycling the HFO-1234yf.

Furthermore, the document WO 2008/008519 describes, in example 5, theseparation of an azeotropic composition of HFO-1234yf and HF byliquid/liquid extraction using an isomer of 1,2,3,3,3-pentafluoropropeneat a temperature of −40° C. The compound used for the extraction ishighly toxic.

The applicant company has now developed a process for the separation ofa composition comprising 2,3,3,3-tetrafluoropropene and HF and for therecovery not only of the 2,3,3,3-tetrafluoropropene but also of the HF.This process does not exhibit the disadvantages of the prior art.

A first subject matter of the present invention is thus a process forthe separation and recovery of 2,3,3,3-tetrafluoropropene and HF from acomposition comprising 2,3,3,3-tetrafluoropropene and HF, characterizedin that it comprises a stage of cooling (separating by settling) saidcomposition in the presence of an added amount of at least one compound(C1) chosen from chlorocarbons, hydrochlorocarbons,hydrochlorofluorocarbons, optionally fluorinated alcohols, optionallyfluorinated ethers, ketones, esters, polyols and hydrofluorinated ethersin order to give an upper phase concentrated in HF and a lower phaseconcentrated in HFO-1234yf and compound C1.

This stage of cooling in the presence of at least one compound C1 makesit possible to obtain an upper phase which is richer in HF with a verysmall amount of HFO-1234yf, which phase is capable of being used withoutany purification stage. The HF thus recovered can be directly recycledto a hydrofluorination reaction stage.

The lower organic phase comprises the compound C1, HFO-1234yf andpossibly organic impurities. This organic phase can be subjected to adistillation stage in order to separate the compound C1 and HFO-1234yf.The compound C1 can be recycled to the cooling stage and/or to thereaction stage resulting in the formation of HFO-1234yf.

The HFO-1234yf/HF molar ratio in the composition to be separated ispreferably between 0.5 and 2.5 and advantageously between 1.1 and 2.1.

The 2,3,3,3-tetrafluoropropene is preferably present in an azeotropic orquasi azeotropic amount with the HF in the composition to be separated.

Advantageously, the composition to be separated originates from ahydrofluorination or dehydrofluorination stage.

The compound C1 to be added to the composition for the cooling stage isa hydrohalocarbon compound which preferably comprises three carbonatoms. Mention may in particular be made of pentachloropropanes, inparticular 1,1,1,2,3-pentachloropropane (HCC-240db),1,1,2,2,3-pentachloropropane (HCC-240aa) and1,1,1,2,2-pentachloropropane (HCC-240ab); tetrachlorofluoropropanes, inparticular 1,1,2,3-tetrachloro-1-fluoropropane (HCFC-241db);trichlorodifluoropropanes; dichlorotrifluoropropanes, in particular1,2-dichloro-3,3,3-trifluoropropane (HCFC-243db); chlorotetrafluoropropanes, in particular2-chloro-1,1,1,2-tetrafluoropropane (HCFC-244bb); tetrachloropropenes,in particular 1,1,2,3-tetrachloropropene (HCO-1230xa) and1,1,1,2-tetrachloropropene (HCO-1230xf); and chlorotrifluoropropenes, inparticular 2-chloro-3,3,3-trifluoropropene (HCFO-1233xf).

Preferably, the compound to be added is the same as that which hasreacted with HF to give the HFO-1234yf or the compound to be added is anintermediate in the hydrofluorination reaction resulting in themanufacture of the HFO-1234yf.

For example, when the HFO-1234yf is prepared by the hydrofluorinationreaction on HCC-240db, the compound C1 is preferably HCC-240db orHCFO-1233xf.

Likewise, when the HFO-1234yf is prepared by the hydrofluorinationreaction on HFO-1233xf, the compound C1 is preferably HFO-1233xf.

When the HFO-1234yf is prepared by the hydrofluorination reaction onHFO-1230xa, the compound C1 is preferably HFO-1230xa or HCFO-1233xf.

When the compound C1 is different from that which has reacted with HF togive HFO-1234yf, the preferred compound C1 is chosen from optionallyfluorinated alcohols, optionally fluorinated ethers, ketones, esters,polyols and hydrofluorinated ethers.

Mention may in particular be made, as alcohol, of those having an alkylgroup of 1 to 5 carbon atoms. The alcohol can also be fluorinated andthe preferred fluorinated alcohol is chosen from the alkyl groups of 1to 3 carbon atoms.

The ketones of formula RCOR′ with R and R′, which are identical ordifferent, each representing an alkyl group of 1 to 5 carbon atoms maybe suitable.

The esters of formula RCOOR′ with R and R′, which are identical ordifferent, each representing an alkyl group of 1 to 5 carbon atoms maybe suitable.

The ethers of formula ROR′ with R and R′, which are identical ordifferent, each representing an alkyl group of 1 to 7 carbon atoms maybe suitable.

The ethers may be partially or completely fluorinated. When the ethersare partially fluorinated, they are denoted by hydrofluorinated ether.

Preference is given, as hydrofluorinated ether, to that having a boilingpoint of between 0 and 250° C., advantageously between 20° C. and 200°C. and more advantageously between 20° C. and 150° C.

Mention may in particular be made of 2,2,2-trifluoroethyl difluoromethylether (HFE-245mf), 1,1,1,2,2-pentafluoroethyl methyl ether (HFE-245mc),1,1,2,2-tetrafluoroethyl methyl ether (HFE-245pc),1,1,2,3,3,3-hexafluoropropyl methyl ether (HFE-356mec) or1,1,1,2,2,2-hexafluorodiethyl methyl ether (HFE-356mff).

The hydrofluorinated ether, such as heptafluoropropyl methyl ether(HFE-7000), nonafluorobutyl methyl ether/nonafluoroisobutyl methyl ether(HFE-7100), nonafluorobutyl ethyl ether (HFE-7200),decafluoro-3-methoxy-4-(trifluoromethyl)pentane (HFE-7300),2-trifluoromethyl-3-ethoxydodecafluorohexane (HFE-7500) and the mixtureof perfluoroisobutyl ethyl ether and perfluorobutyl ethyl ether (20-80%by weight) (HFE-8200), may be an advantage.

The polyols, such as ethylene glycols RO(CH₂CH₂O)_(n)R′ with n between 1and 3 and R and R′, which are identical or different, each representinga hydrogen atom or an alkyl group of 1 to 5 carbon atoms, may besuitable.

The amount of compound C1 to be added can represent from 5 to 95% byweight, with respect to the HFO-1234yf/HF mixture and preferably from 10to 80% by weight, with respect to the HFO-1234yf/HF mixture.

The composition to be separated is preferably cooled to a temperature ofbetween −20 and 40° C. and advantageously to a temperature of between −5and 35° C. The cooling temperature depends both on the nature and on theamount of the compound C1 to be added. Thus, in the case of the additiona small amount of HCC-240db, the temperature of the cooling stage ispreferably within the vicinity of 0° C., whereas it can reach ambienttemperature (that is to say, 25° C.) in the presence of a greater amountof addition of the compound C1.

The pressure at which this cooling stage is carried out is between 0 and40 bar, preferably between 0.3 and 25 bar and advantageously in thevicinity of the pressure of the reaction stage.

In addition to the HFO-1234yf and the HF, the composition to beseparated can comprise organic impurities, such as HCFC-243db,HCFO-1233xf, 1,1,1,2,2-pentafluoropropane (HFC-245cb),1,3,3,3-tetrafluoropropene (HFO-1234ze), 1-chloro-3,3,3-trifluoropropene(HFO-1233zd) and 3,3,3-trifluoropropene (HFO-1243zf).

These impurities are generally byproducts from the reaction stage.

Another subject matter of the present invention is a process for thepurification of the HFO-1234yf. After the cooling stage, the HFO-1234yfis separated from the compound C1 of the organic phase, for example bydistillation. The compound C1 can subsequently be recycled to thecooling stage and/or to the reaction stage when the compound C1 is areactant or an intermediate of the reaction stage resulting in theformation of the HFO-1234yf.

The HFO-1234yf thus separated can subsequently be subjected to apurification stage in order to remove the impurities and possibly tracesof HF.

Thus, when the HFO-1234yf is separated by distillation of the organicphase comprising C1, the gaseous effluent predominantly comprisingHFO-1234yf resulting from the distillation column can be subjected towashing in washing columns comprising water and then comprising aqueoussodium hydroxide solution in order to remove any traces of acidity. TheHFO-1234yf, free from its acidity, can subsequently be dried, compressedand liquefied, and finally purified using several distillation columns,making it possible to remove the light or heavy impurities originatingfrom the preceding stages.

The advantage of the stage of cooling (separated by settling) accordingto the present invention is in part to maximize the recovery of HF andto minimize the amount of HF present in the organic phase, which isreflected by minimization in the effluents comprising HF. It alsoexhibits the advantage of minimizing the amount of HFO-1234yf recycledin the reaction stage in the phase enriched in HF. Furthermore, thisseparating by settling can be carried out at ambient temperature, whichmakes it possible to avoid cooling the mixture to very low temperaturesand using a refrigerated unit, which exhibits a certain advantage interms of energy.

In addition, a subject matter of the present invention is a process forthe manufacture of HFO-1234yf comprising (i) at least one stage duringwhich at least one saturated or unsaturated hydrocarbon compound havingthree carbon atoms and comprising at least one chlorine atom whichreacts with HF in the presence of a fluorination catalyst, (ii) a stageof removal of HCl coproduced during stage (i), (iii) a stage of coolingaccording to the first subject matter of the invention and (iv) at leastone stage of purification of HFO-1234yf of the organic phase obtained in(iii).

Preferably, the saturated or unsaturated hydrocarbon compound havingthree carbon atoms is chosen from HCC-240db, HCFO-1233xf and HCO-1230xa.

The stage of reaction with HF is preferably carried out in the gasphase.

According to a preferred embodiment of the present invention, theprocess for the manufacture of HFO-1234yf comprises (i) at least onereaction stage during which HCC-240db reacts in the gas phase with HF inthe presence of a fluorination catalyst to give a stream comprisingHFO-1234yf and its intermediates, for example HCFO-1233xf, HCl andexcess HF; (ii) a stage of removal of HCl from the stream exiting fromstage (i); (iii) a stage of cooling in the presence of the addition ofthe compound C1, preferably HCC-240db or HCFO-1233xf, to give an upperphase concentrated in HF and a lower phase concentrated in HFO-1234yfand comprising the compound C1; (iv) a stage of separation of theHFO-1234yf from the compound C1 and optionally recycling the compound C1to the cooling stage (iii) or to stage (i); (v) a stage of purificationof the HFO-1234yf; and (vi) optionally recycling of the upper phase richin HF to stage (i).

In the presence of a large excess of HF used in the reaction stage, theprocess for the manufacture of HFO-1234yf according to the presentinvention can comprise, before the stage of removal of HCl, a stage ofdistillation in order to recover a portion of HF which can be recycledto the reaction stage.

FIG. 1 described below represents a preferred embodiment of the presentinvention.

HCC-240db (1) and HF (2), which are optionally preheated, are introducedinto the reactor (101) containing a fluorination catalyst maintained ata temperature of between 300 and 450° C. The stream (102) at the outletof the reactor, comprising HCl, HF, HFO-1234yf, HCFO-1233xf andHFC-245cb, is sent to a first column for distillation of the HF (103) togive, at the column top, a stream (104) comprising HCl, HFO-1234yf, HFand HFC-245cb and, at the column bottom, a stream (105) comprising HF,HCFO-1233xf and HFC-245cb.

The stream (104) is sent to a second distillation column (106) to giveHCl at the top and a stream (107) at the bottom comprising HF,HFO-1234yf and HFC-245cb.

The stream (105) is recycled to the reactor (101).

The decanter (108), maintained at a temperature of between −5 and 35°C., is fed with the stream (107) and with the stream (110) comprisingHCC-240db.

The lower phase (109) of the decanter, comprising HFO-1234yf andHCC-240db, is sent to a distillation column (112) to give, at the top, astream essentially comprising HFO-1234yf (113) and, at the bottom, astream (110) essentially comprising HCC-240db.

The stream (110) is recycled to the reactor (101) and/or to the decanter(108).

The upper phase (111) of the decanter, enriched in HF, is recycled tothe reactor (101).

The stream (113) is sent to the washing columns (114) to give, at thetop, a stream (115) freed from any acidity.

The stream (115) is finally sent to the purification stage (116) to givepure HFO-1234yf.

Experimental Part

A liquid composition containing 40 mol % of HF and 60 mol % ofHFO-1234yf (i.e., 89.5% by weight) is cooled to atmospheric pressure ata temperature slightly greater than 15° C. There is no separation bysettling.

At a temperature of less than 15° C., a lower organic phase is obtainedwhich comprises more than 92% by weight of HFO-1234yf and an upper phaseis obtained which comprises only 71% by weight of HF.

At −30° C., the upper phase contains only 78% by weight of HF and 22% byweight of HFO-1234yf, which remains very high. The lower organic phasecontains 98.5% by weight of HFO-1234yf and 1.5% by weight of HF. Theefficiency of the separation by settling is thus mediocre, even at lowtemperature.

EXAMPLES ACCORDING TO THE INVENTION Example 1

A liquid composition containing 32.6% by weight of HFO-1234yf, 3.9% byweight of HF (HFO-1234yf/HF molar ratio=1.48) and 63.5% by weight ofHCC-240db is cooled.

At a cooling temperature of 20° C., a lower organic phase is obtainedwhich comprises 0.2% by weight of HF and an upper phase is obtainedwhich comprises 88% by weight of HF and 10% by weight of HFO-1234yf.

At a cooling temperature of 0° C., a lower organic phase is obtainedwhich comprises 0.1% by weight of HF and an upper phase is obtainedwhich comprises 89% by weight of HF and 9% by weight of HFO-1234yf.

Example 2

A liquid composition containing 36.5% by weight of HFO-1234yf, 4.3% byweight of HF (HFO-1234yf/HF molar ratio=1.5) and 59.2% by weight ofHCC-1230xa is cooled.

At a cooling temperature of 20° C., a lower organic phase is obtainedwhich comprises 0.2% by weight of HF and an upper phase is obtainedwhich comprises 86% by weight of HF and 11% by weight of HFO-1234yf.

At a cooling temperature of 0° C., a lower organic phase is obtainedwhich comprises 0.15% by weight of HF and an upper phase is obtainedwhich comprises 87% by weight of HF and 11% by weight of HFO-1234yf.

Example 3

A liquid composition containing 38.1% by weight of HFO-1234yf, 4.5% byweight of HF and 57.4% by weight of HCFC-243db is cooled.

At a cooling temperature of 20° C., a lower organic phase is obtainedwhich comprises 0.1% by weight of HF and an upper phase is obtainedwhich comprises 85% by weight of HF and 9% by weight of HFO-1234yf.

At a cooling temperature of −20° C., a lower organic phase is obtainedwhich comprises less than 0.1% by weight of HF and an upper phase isobtained which comprises 88% by weight of HF and 9% by weight ofHFO-1234yf.

Example 4

A liquid composition containing 43.6% by weight of HFO-1234yf, 5.2% byweight of HF and 51.2% by weight of HCFC-1233xf is cooled.

At a cooling temperature of 0° C., a lower organic phase is obtainedwhich comprises 2% by weight of HF and an upper phase is obtained whichcomprises 77% by weight of HF and 11% by weight of HFO-1234yf.

Example 5

A liquid composition containing 40.4% by weight of HFO-1234yf, 4.8% byweight of HF and 54.8% by weight of HCFC-244bb is cooled.

At a cooling temperature of 20° C., a lower organic phase is obtainedwhich comprises 1.5% by weight of HF and an upper phase is obtainedwhich comprises 82% by weight of HF and 10% by weight of HFO-1234yf.

At a cooling temperature of 0° C., a lower organic phase is obtainedwhich comprises 1% by weight of HF and an upper phase is obtained whichcomprises 84% by weight of HF and 9% by weight of HFO-1234yf.

The invention claimed is:
 1. A process for the manufacture of2,3,3,3-tetrafluoropropene, comprising (i) at least one reaction stageduring which at least one saturated or unsaturated hydrocarbon compoundhaving three carbon atoms and comprising at least one chlorine atomreacts in the gas phase with HF in the presence of a fluorinationcatalyst to give a stream comprising 2,3,3,3-tetrafluoropropene andintermediates of 2,3,3,3-tetrafluoropropene, HCl and excess HF; (ii) astage of removal of HCl from the stream exiting from stage (i); (iii) astage of cooling said stream exiting from stage (ii) in the presence ofan added amount of at least one compound (C1) selected from the groupconsisting of chlorocarbons, hydrochlorocarbons,hydrochlorofluorocarbons, alcohols, fluorinated alcohols, ethers,fluorinated ethers, ketones, esters, polyols and hydrofluorinated ethersin order to separate an upper phase rich in HF from a lower organicphase rich in 2,3,3,3-tetrafluoropropene and compound C1, whereby saidseparating occurs by settling; (iv) a stage of separation of the2,3,3,3-tetrafluoropropene from the lower phase; and (v) a stage ofpurification of the 2,3,3,3-tetrafluoropropene.
 2. The process asclaimed in claim 1, characterized in that it comprises a stage ofdistillation of HF before the stage of removal of HCl.
 3. The process asclaimed in claim 1, wherein in stage (iii), the2,3,3,3-tetrafluoropropene/HF molar ratio is between 0.5 and 2.5.
 4. Theprocess as claimed in claim 1, wherein in stage (iii), the amount ofcompound C1 to be added represents from 5% to 95% by weight, withrespect to the HFO-1234yf/HF mixture.
 5. The process as claimed in claim1, characterized in that the temperature in stage (iii) is between 20and 40° C.
 6. The process as claimed in claim 1, wherein the saturatedor unsaturated hydrocarbon compound having three carbon atoms is chosenfrom 1,1,1,2,3-pentachloropropane, 1,1,2,3-tetrachloropropene and2-chloro-3,3,3-trifluoropropene.
 7. The process as claimed in claim 1,wherein the compound C1 is selected from the group consisting of1,1,1,2,3-pentachloropropane, 1,1,2,3-tetrachloro-1-fluoropropane,1,2-dichloro-3,3,3-trifluoropropane, 1,1,2,3-tetrachloropropene and2-chloro-3,3,3-trifluoropropene.
 8. The process as claimed in claim 1,wherein the compound C1 is selected from the group consisting ofalcohols ROH, ketones RCOR′, esters RCOOR′, with R and R′, which areidentical or different, each representing an alkyl group of 1 to 5carbon atoms, and ethers ROR′, with R and R′, which are identical ordifferent, each representing an alkyl group of 1 to 7 carbon atoms. 9.The process as claimed in claim 1, wherein the compound C1 is the sameas that which reacted with HF in the hydrofluorination stage.
 10. Theprocess as claimed in claim 1 wherein the part enriched in HF after thecooling stage is recycled to the hydrofluorination stage.
 11. Theprocess as claimed in claim 1, characterized in that the organic part,after separation of the 2,3,3,3-tetrafluoropropene is recycled to thecooling stage and/or to the reaction stage.